It is adviseable to use the spring preload only to adjust the ride height to the correct specification. Do not try to solve a bottoming out problem by adding spring preload. This will likely bring the ride height out of specification and still not solve the bottoming out problem.
If you are having problems with the shock absorber bottoming out, add compression damping with the electronic adjuster or change the spring to a stiffer one (the standard spring is 48 N/mm (274 lbs/inch), Yamaha is also offering a 54 N/mm (308 lbs/inch)). If this does not solve your bottoming out problem it might be a good idea to get the shock re-valved and re-springed to the scandinavian spec (more damping and 70 N/mm (400 lbs/inch) spring).
The rebound adjuster DOES affect the compression damping, though not very much. The rebound adjuster is an adjustable needle/jet combination that bleeds oil flow off from the main valve instead of letting it pass through the main valve. The more oil flow that is bleeded off the less damping is produced. This bleed works in both directions and therefore the rebound adjuster adjusts both the compression and rebound damping. Since the main rebound valve is usually quite a lot stronger than the main compression valve, the rebound damping is adjusted quite a lot more than the compression damping.
